Recently, the calibration of three-dimensional vibration sensor is usually based on a single dimension vibration calibration system, which calibrates the three axes of the sensor one after another. Inevitably, this method consumes too much time and complicates the data processing system. In the meantime, considering the cross-axis coupling of the three-dimensional sensor, it is hard to obtain the sensitivity matrix, which describes the coupling relations between the three axes of the sensor based on this method. So, development of a three-dimensional standard vibrator, which could output vibration signals to excite the three axes of the three-dimensional sensor synchronously, has important theoretical and practical significance on the development of the calibration technology for vibration sensor and the progress of the related industry technology.
The Chinese patent CN 102364316 B announces a three-dimensional standard vibrator based on a latch-type decoupling device. The vibrator consists of a base, three single-dimensional electromagnetic vibrators along X, Y, and Z axis (X and Y axes represent the two horizontal directions perpendicular to each other and Z axis represents the vertical direction) and a three-dimensional vibration platform. Each of the single-dimensional vibrators is connected with the three-dimensional vibration platform through a motion decoupling device. The motion decoupling device consists of the first framework and the second framework, which are intersected with each other. The two frameworks are all comprised of the outer frame, the inner frame, the first and second lateral frames between the outer and inner frames. The outer frame is opposite to the inner frame, and the inner frame from one of the frameworks is inserted into the other framework. The inner frame of the first framework is drilled with gas channels and vent holes. The two ends of all the vent holes are connected with the gas channels and the outside atmospheres, respectively. The second framework is installed with its inner and outer frames both have little intervals to the inner frame of the first framework, and the intervals could form the aerostatic guide rails for the inner frame of the first framework. There is a gap between the inner frame of the second framework and the outer frame of the first framework to avoid interfering of the two frameworks. The gas channels are connected with the outside pressured gas sources. The two outer frames of the first framework and the second framework are connected with the electromagnetic vibrator and the three-dimensional vibration platform, respectively. The latch-type structures and the technique of aerostatic gas-floating are utilized in the vibrator to realize force transmissions and motion decoupling for the three-dimensional vibrations.
The shortcomings of the proposed vibrator are as follows. 1) The required accuracy of the assembling is excessively high since the first and second frameworks are mounted on the vibrator and the three-dimensional vibration platform respectively and the two frameworks are inserted with each other with latch-type structure. Besides, the area of the gas film is restricted when it is formed in the interval between the first and second frameworks, and the second framework increases the mass of the three-dimensional vibration platform. 2) Since the latch-type structure pulls the three-dimensional vibration platform when the vibrator vibrates back and forth, it is prone to generate structural deformations and bring great loads for the vibrator. 3) Conventionally, an air cavity is designed to improve the orifice restricted bearings' loading capacity. However, the existence of the air cavity will inevitably generate “pneumatic hammer” phenomenon in a specified frequency range and reduce the loading stability and upper limit of working frequency for the aerostatic gas-floating system. In addition, restricted by the orifice size and machining accuracy, it is difficult to guarantee the uniformity of the loading capacity among each of the orifices. The non-uniform loading will make the three-dimensional vibration platform tilt or rotate, and do harm to the motion decoupling of the three-dimensional standard vibrator.